[Rathji]

I don't know if dual band is worth it, it would depend on your usage. What it allows you to do is set exclusive use for each band for individual programs on your computer (if you have a dual band card as well), ie torrent on one band and surf on another band. This type of usage won't have that much of an effect, since any bottle necking from it will likely occur at your internet connection. I have had this work wonders at the University where network traffic itself is what hampers your connection.

Other than that the only reasons I see that it would be worth it, is in a situation where you are planning on streaming large amounts of media/data on the network on a constant basis. This would allow for you to avoid one messing with the other. I don't have the ability to stream media myself though, so I am mostly just guessing that this would be helpful.

Also, if you are having large amounts of interference on one band that is noticeably affecting your speeds, you might be able to switch bands to avoid it, but that's just a guess really.

As for the Airport Extreme, I have never used it personally, but it is pretty much the router with the most features of any I have seen. You can get a comparable router from DLink and Linksys I think, for a reduced price, but when I made the post I didn't want to search through product pages to find the right one. I think, and I might be wrong, that you can add an external HDD to the network through the Airport and it will be able to function as a Time Machine, but I am not sure on that at all though.